SV: [mapserver-users] Shapefiles with islands

[Steve Grey]

Lars,

Can you give us an example, or extract of, a location where the rendering
problems are?  Having trouble with some of the terminology too -
multipolygons are multipart polygons, each polygon of which is a single part
but can be a donut with multiple holes?

Steve




2009/10/22 Lars Westerlind <lars.westerlind at enera.se>

>
> Hello Steve,
> Thanks for your attention.
> I fully agree that there is nothing yet indicating a bug in mapserver. The
> shapefiles I've inspected just lack the inner polygons, which certainly are
> available when editing open street data at their site; Mapserver can't
> guess, can it?
>
> But if I got it right you answered a question I've got but not expressed.
> You say Mapserver would handle a multipolygon shapefile correctly, that is,
> there would be no need to make special entries in the mapfile for the
> islands; they would just be drawn as holes in the lakes automatically? I was
> thinking I had to draw lakes first, and then islands in lakes.
>
> If so I'm even more curious why nobody have put the pieces together. Maybe
> it's about competition? I guess I'll have to leave the issue until when/if
> I'll get time to do learn how to do my own data extracts, or other sources
> will be available.
>
> /Lars
>
>
> -----Ursprungligt meddelande-----
> Från: Steve Lime [mailto:Steve.Lime at dnr.state.mn.us]
> Skickat: 21 October 2009 17:11
> Till: Lars Westerlind; mapserver-users at lists.osgeo.org
> Ämne: Re: SV: [mapserver-users] Shapefiles with islands
>
> I'm not using the OpenStreetMap data but am rendering and querying lots
> of complex lake
> polygons with multiple outer rings (basins) and inner rings (islands).
> You need not do anything
> special. Sounds like a data production problem more so than a MapServer
> bug. Here's a sample:
>
>
>
> http://maps.dnr.state.mn.us/cgi-bin/mapserv56?mode=map&map=/usr/local/mapserver/apps/mr/landview/landview.map&mapext=523963.26347152865+5289818.927668251+570217.999745758+5313957.83079347&mapsize=1006+525&layers=lakes+roads+bdry_munipy3&layer=bdry_statepy2&map.imagetype=aggpng24
>
> All the lakes are multi-polygons...
>
> For example, if islands are represented as individual features and not
> inner rings of lake
> polygons then you might be running into draw order issues. MapServer
> renders the features
> in the order they show up in the shapefile. I suppose it's possible
> then that islands might
> be getting drawn before the lake (which has no holes). If that's the
> case (try drawing
> outlines only and no fill) then you'd need to sort the data based on
> some sort of land
>  vs. water attribute so that lakes are drawn first then the islands on
> top.
>
> >>> On 10/21/2009 at 12:33 AM, in message
> <2349CC72A0B01C4FAA4FFAE6C735E1DDE293AD at enerasrv01.Enera.local>, "Lars
> Westerlind" <lars.westerlind at enera.se> wrote:
> > So,
> > How is the lack of response to be interpreted? Nobody render islands
> in
> > lakes? Everybody make their own data extracts? Or there are other
> (for me)
> > hidden sources of information?
> >
> > /Lars
> >
> >
> > -----Ursprungligt meddelande-----
> > Från: mapserver-users-bounces at lists.osgeo.org
> > [mailto:mapserver-users-bounces at lists.osgeo.org] För Lars Westerlind
> > Skickat: 19 October 2009 11:43
> > Till: mapserver-users at lists.osgeo.org
> > Ämne: [mapserver-users] Shapefiles with islands
> >
> > Hi,
> > I wonder if anyone renders islands in lakes? I use OpenStreetMap
> Data,
> > where lakes are tagged as multipolygons, with islands as inner
> polygons.
> > The source I use, mainly the "Mapserver recommended" cloudmade make
> > simple extracts where those inner polygons are simply skipped,
> AFAIU.
> > Looks rather funny for islands that are large enough to keep some
> > roads...
> >
> > So, what is recommended? Should I make my own OpenStreetMap extracts
> for
> > this purpose? Or does anyone have any other good sources?
> >
> > BTW,
> > Do I understand correctly that multipolygon files must be converted
> in
> > order to be possible to handle by mapserver? I mean, inner polygons
> > should have at least an extra column in the DBfile, telling it's
> level,
> > or such?
> >
> > Regards,
> > Lars
> >
> >
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